The present application relates to a battery pack having a non-aqueous electrolyte secondary battery housed therein, and a method of manufacturing the same, and in particular to a battery pack realizing high volumetric efficiency.
In recent years, a variety of portable electronic instruments, such as camera-integrated VTR (video tape recorder), mobile phone and laptop computer have become popular, under continuing efforts of downsizing and weight reduction. Accordingly, demands on batteries used as power sources of the portable electronic instruments are rapidly growing, raising further demands on battery design aimed at making the battery lighter, thinner, and more efficient in use of housing space in the instruments, in order to realize downsizing and weight reduction of the instruments. Lithium ion secondary battery, having large energy density and large output density, is most preferable as the battery capable of satisfying this sort of demands.
Among others, lithium ion polymer secondary battery using a gel-type polymer electrolyte is widely used, aimed at preventing leakage of the electrolyte which raises issues in a case where the related art liquid electrolyte is used. In the lithium ion polymer secondary battery, electrode terminals are connected, a strip-like positive electrode and a negative electrode having a polymer electrolyte coated on both surfaces thereof are stacked while placing a separator in between, and then rolled in the longitudinal direction to fabricate a battery element. The battery element is then packaged by a laminating film to thereby produce a battery cell, and the battery cell is then housed in a resin mold case to thereby produce a battery pack.
Alternatively, Japanese Patent Application Publication No. JP 2005-166650 (Patent Document 1) describes a battery pack which is no more necessarily to house a battery cell in a resin molding case and improved in the volumetric efficiency.
A configuration of a battery pack 1 described in Patent Document 1 is shown in FIG. 1. The battery pack 1 is composed of a battery cell 10 provided with a battery element, a circuit board 4 connected to a positive electrode terminal 2a and a negative electrode terminal 2b (occasionally referred to as “electrode terminals 2” hereinafter, unless otherwise specifically limited) lead out from the battery cell 10, a top cover 5a housing the circuit board 4 and engaged with the opening at lead out side (occasionally referred to as “top side”, hereinafter) of the electrode terminal 2 of the battery cell 10, and a bottom cover 5b engaged with the opening at a side opposite to a top side of the battery cell 10 (occasionally referred to as “bottom side”, hereinafter).
FIG. 2A to FIG. 2C show a state where the battery pack 1 is under manufacturing process. FIG. 2A is a top view of the battery cell 10 under the process of manufacturing, FIG. 2B is a side elevation of the battery cell 10 shown in FIG. 2A as viewed laterally from the right side thereof, and FIG. 2C is a side elevation of the battery cell 10 shown in FIG. 2A as viewed from the bottom side thereof.
As shown in FIGS. 2A to 2C, the battery cell 10 is configured as having a battery element 9 provided with a positive electrode terminal 2a and a negative electrode terminal 2b, packaged by a rectangular hard laminating film 6, and by a rectangular soft laminating film 7 having long sides almost equal to those of the hard laminating film 6 and short lines almost equal to or slightly smaller than those of the hard laminating film 6.
Sectional views of the hard laminating film 6 and the soft laminating film 7 are shown in FIG. 3A and FIG. 3B. The hard laminating film 6 composing the outermost package of the battery pack 1 has, as shown in FIG. 3A, a metal layer 6a composed of a hard metal material, an outer resin layer 6b formed on one surface of the metal layer, and an inner resin layer 6c formed on the other surface of the metal layer. On the other hand, as shown in FIG. 3B, the soft laminating film 7 has a metal layer 7a composed of a soft metal material, an outer resin layer 7b formed on one surface of the metal layer, and an inner resin layer 7c formed on the other surface of the metal layer.
The outer resin layer 6b and the outer resin layer 7b function as surface protection, and are typically composed of nylon (Ny) or polyethylene terephthalate (PET). On the other hand, the inner resin layer 6c and the inner resin layer 7c have function of bonding the hard laminating film 6 with the soft laminating film 7, or bonding the hard laminating film 6 with the top cover 5a and the bottom cover 5b, and is made of cast polypropylene (CPP).
The soft laminating film 7 has a recess 8 for housing the battery element 9, which is formed by drawing, for example. The hard laminating film 6 is stacked on the soft laminating film 7 such that the opening of the recess 8 is covered after the battery element 9 is housed in the recess 8. The hard laminating film 6 is stacked at a position slightly shifted rightward with respect to the soft laminating film 7, for example. In this way of stacking of the hard laminating film 6 and the soft laminating film 7, as shown in FIG. 2A, there are produced a right region in which only the hard laminating film 6 is positioned and the inner resin layer 6c is exposed, and a left region in which only the soft laminating film 7 is positioned and the inner resin layer 7c is exposed. The portion where the hard laminating film 6 and the soft laminating film 7 overlap is fused by heating, and thereby surrounding four lines of the battery element 9 are sealed.
Both of the left and right ends of the hard laminating film 6 and the soft laminating film 7 are folded so as to wrap the recess 8, and thereby the battery cell 10 having the openings on both ends is fabricated. FIG. 4 shows a cross-section of a portion where the hard laminating film 6 and the soft laminating film 7 abut with each other. As shown in FIG. 4, the films are molded such that short lines of both sides of the hard laminating film 6 are abut to slight space and face each other with the space in between, and short lines of both sides of the soft laminating film 7 are abut to slight space and face each other with the space in between. In this stage, a heat seal adhesive film 11, composed of a resin material, for example, is provided on the outer bottom surface of the recess 8. After the hard laminating film 6 and the soft laminating film 7 are deformed so as to wrap the battery element 9, the battery cell 10 is heated so as to melt the heat seal adhesive film 11, and whereby the outer bottom portion of the recess 8 and both end portions of the soft laminating film 7 are bonded.
In this process, the right region having only the hard laminating film 6 positioned therein and the left region having only the soft laminating film 7 positioned therein are bonded at the same time. By overlapping the hard laminating film 6 and the soft laminating film 7 while being slightly shifted from each other, the inner resin layer 6c of the hard laminating film 6 and the inner resin layer 7c of the soft laminating film 7 are opposed at the outer bottom surface of the recess 8, and are bonded by having a certain width.
In the battery cell 10, a positive electrode terminal 2a and the negative electrode terminal 2b are lead out from the sealed portion of the hard laminating film 6 and the soft laminating film 7. In this configuration, the portions where the positive electrode terminal 2a and the negative electrode terminal 2b come into contact with the hard laminating film 6 and the soft laminating film 7 are respectively provided with resin chips 3a and 3b. The resin chips 3a and 3b are excellent in adhesiveness with each metal material composing the positive electrode terminal 2a and the negative electrode terminal 2b, and can improve the adhesiveness of the positive electrode terminal 2a and the negative electrode terminal 2b, with the hard laminating film 6 and the soft laminating film 7.